1. Technical Field
The present invention relates to shutoff valves. More particularly, the present invention relates to shutoff valves for use with compressed fluid tanks, such as natural gas tanks or cylinders as used on vehicles. Specifically, the present invention relates to a shutoff valve having an inverted stem/seat design with a removable stem designed to include a high performance polymer tip for use with a compressed fluid cylinder where the high performance polymer tip reduces the likelihood of damage to the valve seating area of the shutoff valve, where the removable stem with the high performance polymer Up thereon makes replacement quick and easy should the soft tip become damaged, and where the inverted stem/seat design positions the stem and high performance polymer tip such that the pressurized natural gas acts in unison with the threaded stem tip in seating the stem rather than acting against the stem.
2. Background Information
Since the advent of automobiles and other vehicles at the beginning of the twentieth century, substantially all vehicles have been powered by internal combustion engines. However, it has long been known that natural gas is a cleaner burning fuel and that sufficient natural gas for long trips may be stored under pressure in a compressed state within a high-pressure gas storage cylinder. This coupled with the recent trend toward more environmentally friendly products, further coupled with increased gasoline prices since the 1970's as well as improved cost efficiency surrounding natural gas combustion, has resulted in natural gas combustion growing in popularity because it provides a cost efficient and environmentally friendly alternative to the gasoline engines presently wide spread.
As a result of the above mentioned factors, the use of compressed natural gas has begun to grow in popularity. In recent years, a significant number of large urban vehicles, such as buses, city trucks and garbage trucks, and a smaller but growing number of trucks and passenger vehicles, have been newly built or converted to natural gas with relative success using off the shelf, high pressure gas storage cylinders and industrial valves.
However, the emergence of compressed natural gas (CNG) as the preferred clean energy fuel for large urban vehicles has more rapidly fueled the interest in CNG. Specifically, this emergence of CNG in the large urban vehicle area has created a need for valves and other fuel system components specifically designed or tailored for the applications. Previously the need for vehicle CNG storage cylinder valves has been satisfied by using various off the shelf valves for different applications, including industrial gas valves; however, this practice that has proven less than ideal, for a number of reasons including the following.
First, these industrial gas valves are usually manufactured from brass forgings. The forging dies that are required to make the brass forging are very expensive to change or modify. For this reason, brass forgings tend to be made and sold on a "one size fits all" basis. The result is that since it is so cost prohibitive to "tailor" these valves to individual vehicle needs, often industrial gas valves that are neither designed nor optimized for compressed natural gas uses are used anyway.
Second, because of the high pressure performance requirements of the natural gas environment, it has always been a requirement that these industrial valves are rather "beefy," i.e., rather heavy and bulky, and as a result require a relatively large "space envelope", i.e., the area in which the valve is positioned. One of the reasons such a large space envelope is required is because sufficient space must be provided in which to rotate a hand wheel with a user's hand wrapped therearound as would be required, when desired, to sufficiently tighten the valve to assure proper and complete shut off. In application, this space envelope is required to be quite large because a large hand wheel is required to supply the necessary torque to allow opening and closing of the standard stainless steel industrial valve at full pressure of often up to 5000 or more psi. Overall, the torque required is quite substantial and thus a large hand wheel is used since the larger hand wheel requires less leverage to supply the necessary torque to open and close the valve. The end result is a large space envelope thereby allowing sufficient room to operate the valve therein. Clearly, this large space envelope reduces space that would otherwise be available for increased gas storage which is extremely desirable for greater vehicle range between fuelings.
Third, a process referred to as "fast fill" has become popular when filling the CNG cylinders, but this process often leads to damaged valves. Basically, "fast fill" is where the shutoff valves on a number of CNG cylinders that are fluidly connected in series are all opened via their inlet and outlet ports such that all of the cylinders simultaneously fill from a large high pressure CNG fueling station. The "fast fill" process is economically attractive and is thus in increased demand because of its rapid ability to fill all of the cylinders in series to the same pressure level.
However, this process has one prevalent downfall in that the relatively high gas velocity of "fast fill" gas streams often breaks free any loosely held metal chips or debris within the fuel lines and moves the particles through the fuel system. Some of this hard metallic debris comes to rest on individual tank shut off valve seats. When the valve seats are closed by receiving the stem, this hard metallic debris is pinned between the stem and seat and often causes the valve to leak because proper seating typically cannot be achieved. Furthermore, the operator often attempts to "overpower" the debris by applying additional torque to the valve hand wheel, which due to its often large size is often capable of supplying extremely high levels of torque that will frequently result in permanent damage to the valve's "close tolerance" metal stem and seat. When permanent damage is done to either the metal stem or seat, this condition usually requires prompt attention in the form of priority replacement of the entire leaking valve--a situation that is both time consuming and expensive, and can be very disruptive to the daily use routine for vehicles in public service such as transit buses or garbage trucks.
Overall, the current designs of shutoff valves being used on CNG cylinders for use with vehicles are not tailored to the specific cylinder and vehicle designs, have oversized hand wheels that decrease gas storage space of the cylinder and provide means for placing damaging levels of torque upon the valve stem against the seat as needed to supply sufficient torque to seat the stem under high pressure conditions, typically require complete removal of the entire valve from the cylinder for repair and/or replacement, and are solely reliant on the stem mechanism to seat the stem to withstand high pressure without leaking.